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41.
M. S. Hill 《Marine Biology》1996,125(4):649-654
Several species of boring sponges harbor symbiotic zooxanthellae, and it is believed that the symbiont enhances boring activity of host sponges. This hypothesis was tested using manipulative field experiments to assess the effect of intracellular zooxanthella populations on boring rates of the tropical sponge Anthosigmella varians forma varians. Portions of sponge were attached to 60 calcium carbonate blocks of known weight. Three sets of 10 blocks were grown at high light levels and three sets of 10 blocks were grown at low light levels for 105 d in the Florida Keys, Florida, USA. Boring rates, growth rates (lateral growth and within-substratum tissue penetration), and zooxanthella populations were measured at the end of the experiment. Absolute rates of boring and growth of A. varians forma varians were significantly greater when zooxanthella densities were higher. Boring rate and tissue penetration related to final surface area of sponge attachment was also enhanced when zooxanthella densities were higher, suggesting that the symbiont plays a physiological role in the decalcification process. This is in contrast to the role that zooxanthellae play in coral hosts. Based on the results of this study, it appears that the presence of zooxanthellar symbionts has important ecological and life-history consequences for host sponges. Ability to laterally overgrow competitors will be correlated with the size and activity of zooxanthella populations. In addition, the fitness of host sponges will be enhanced by algal symbionts, since greater penetration within substrata will result in an increase in production of tissue that can be converted into storage, feeding and reproductive functions. 相似文献
42.
43.
Vegetation: a sink for atmospheric pollutants 总被引:14,自引:0,他引:14
A C Hill 《Journal of the Air Pollution Control Association》1971,21(6):341-346
44.
45.
B. J. Hill 《Marine Biology》1976,34(2):109-116
The natural diet, rate of foregut clearance and diurnal activity of the crab Scylla serrata were determined. The gut volume is related to size of crab as gut volume (ml)=0.07e0.033x
, where x=carapace width in millimetres. Fifty per cent of crabs collected in Australia and South Africa contained molluscan remains and about 21% contained crustacean remains — chiefly grapsid crabs. Fish remains were rarely found, and it was concluded that S. serrata does not normally catch mobile forms such as fish and penaeid prawns. Gut clearance of organic tissue was rapid and almost complete after 12 h. Fish bone was retained for a mean time of 2 to 3 days, and shell for 5 to 6 days. Time-lapse photography, using infra-red light, was used to record activity. Visible light flashes reduced activity. S. serrata remained buried during the day, emerging at sunset to spend the night feeding, which occurred intermittently even when unlimited food was available. If no food was present the amount of time spent on the substrate surface was halved. 相似文献
46.
B. J. Hill 《Marine Biology》1975,32(2):119-126
Populations of the crab Scylla serrata (Forskal) were studied in two South African estuaries from 1971 until 1974. One estuary was open to the sea, the other was closed by a sandbar. Population density in the closed estuary was estimated by means of mark-release-recapture data from tagged crabs. The population of S. serrata was estimated as 1 crab/124m2 and the production at 3.4 g/m2/annum. Catch per unit effort data from the closed estuary indicated a natural mortality of 41% in the crabs' second year and 60% in the third. Growth was studied in both estuaries by means of size-frequency analysis and from tagging returns. Growth was rapid in the first 12 to 15 months, when the crabs attained a carapace width of 80 to 160 mm. Thereafter growth slowed, and after 3 years crabs were between 140 and 180 mm in carapace width. Females mated in summer at a carapace width of 103 to 148 mm, males at 141 to 166 mm. After mating, females migrated out of both estuaries into the sea. 相似文献
47.
Sexual selection and cuckoldry in a monogamous songbird: implications for sexual selection theory 总被引:11,自引:0,他引:11
Geoffrey E. Hill Robert Montgomerie Christina Roeder Peter Boag 《Behavioral ecology and sociobiology》1994,35(3):193-199
Sexual selection is generally assumed to be weaker in monogamous than in polygynous animals. Recently, though, extra-pair fertilizations have been hailed as an important force in generating variance in reproductive success among males in socially monogamous species, thereby increasing the intensity of sexual selection. To see if extra-pair copulations contribute to variance in male reproductive success in the house finch (Carpodacus mexicanus), we used DNA fingerprinting to determine the paternity of chicks from 35 nests. This species is a socially monogamous passerine in which plumage brightness serves as a sexually selected indicator of male quality. Out of 119, nestlings 10 (8.3%) were fathered by a male other than the attending male, but cuckoldry occurred randomly with respect to the plumage colouration, size, or age of the attending male. Thus extra-pair fertilizations do not generate variance in male reproductive success with respect to plumage colour. On the other hand, a strongly male-biased sex ratio and asynchronous breeding by females may generate substantial variance in male reproductive success and could explain the evolution of ornamental colouration. 相似文献
48.
In Deception Bay, northern Australia, during 1979–1981, a study was made of the distribution of Scylla serrata (Forskal) in an area having a broad intertidal zone. Juveniles (20 to 99 mm carapace width) were resident in the mangrove zone, remaining there during low tide. The majority of subadult crabs (100 to 149 mm) migrated into the intertidal zone to feed at high tide and retreated to subtidal waters at low tide. Adults (150 mm and larger) were caught mainly subtidally and only small numbers were captured in the intertidal at high tide. Few crabs were captured in the coolest months (May to August). Adults were captured on the flats mainly in the warmest months (January to April), but subadults could be captured over the entire summer (September to March). Juveniles were found in the upper intertidal throughout the year. 相似文献
49.
B. J. Hill 《Marine Biology》1974,25(1):21-24
The tolerances of the first zoeal stage of the crab Scylla serrata (Forskal) have been investigated in 64 different temperature-salinity combinations. Exposure to temperatures above 25°C or to salinities below 17.5 caused considerable mortality; therefore, zoeae are unsuited to estuarine conditions. The larvae can tolerate temperatures down to 5°C is they are inactive below 10°C. It is suggested that 10°C is probably a lower limit and that female crabs which migrate to sea to release their eggs do not enter water with a temperature below 12°C. Hydrological conditions along the south-east coast of Africa indicate that females would, therefore, migrate less than 10 km offshore. 相似文献
50.
A field and laboratory study in 1984–1985 using the foregut contents of crabs caught in Moreton Bay, Queensland, when trawling was underway, showed that animals discarded from trawls constituted about 33% of the diet. Portunus pelagicus can fill its foregut in about 8 min and clear it completely of tissues in about 6 h, except for fish bone which requires about 24 h. P. pelagicus used a zigzag search pattern to find food and moved towards it at a mean point-to-point speed of 290 m h-1 (8 cm s-1). Underwater still photography on the trawl grounds showed that P. pelagicus was the most common scavenger attracted to a bait that simulated trawl-discards, and that it was most active at dusk. Trawler-discards at periods of high food demand in summer may allow larger populations of P. pelagicus to exist than would otherwise occur. 相似文献